In the past, where relatively large energy impulses have been required to operate a fastener driving tool, such as an industrial nailer or stapler, it has been common practice to power such tool pneumatically. Such tools are capable of driving a 3″ or longer nail, or staple, into framing wood such as 2×4s, for example. However, pneumatic driving tools require an on-site air compressor, which is often unavailable or not desired. Also, dragging the pneumatic umbilical is often an impediment to the user.
Corded AC electrical fastener driving tools are often used instead of pneumatic power since electrical power is more often available than air compressors. In particular, much effort has been expended in the prior art in providing heavy duty, high powered, fastener driving tools employing a flywheel as a means of delivering kinetic energy sufficient to drive a heavy duty fasteners. Examples of such systems are disclosed in U.S. Pat. Nos. 4,042,036; 4,121,745; 4,204,622; 4,298,072; and 5,511,715. Use of a flywheel is an attempt to limit the large current draws to actuate a solenoid to drive a fastener. A DC motor is activated over a non-instantaneous period and then the kinetic energy thus developed in the flywheel is clutched to the driver in an “energy dump”.
While such corded electrical fastener driving tools may perform well, in many instances an AC outlet is not available. Even if an AC outlet is available, many users find dragging the electrical cord to be an impediment to use. To address these preferences, it is further known to employ a portable power source such as a battery, such as solenoid-operated fastener driving tools. These portable fastener driving tools are primarily used in light-duty applications such as in driving one inch brad nails, for example, rather than the larger 2″ to 4″ staples or nails used in framing.
One approach to an efficient portable electrically driven tool is a multiple impact tool, such as described in U.S. Pat. No. 4,625,903, wherein a linear inertial member is repeatedly raised by a cam against a compression spring and released to impact a fastener. An electrical motor and portable battery pack are operated in a more efficient manner by running the motor for a period of time rather than providing a surge of power to a device such as a solenoid. The relatively small amount of energy stored in the spring each cycle typically requires a large number of impacts to drive a staple or nail into a workpiece. During this time, the user is required to maintain an appropriate position and force on the fasten and to gauge the appropriate length of time to achieve the desired depth. However, while the multiple impact tool is efficient and effective in driving fasteners, some users prefer a single driving action comparable to pyrotechnic or compressed air systems. The multiple impact tools also can damage a wood surface due to the vibrations the tool generates while stroking.
It would be desirable to use a battery to power a flywheel operated hand tool to provide a portable fastener driver that can drive larger fasteners in a single drive. However, using a battery has been thwarted by a number of challenges. First, each specific application generally requires a fastener drive assembly and motor customized for the type of fastener. In particular, the size of flywheel, the desired rotary speed of the flywheel, and the type of electric motor to accelerate the flywheel to the desired rotary speed are generally specifically sized for the type of fastener and work piece into which the fastener is typically driven. Thus, each specific application was thought to require a custom control module, with the increased costs of design, manufacture and support.
Even assuming that various types of fasteners could then be used with a family of flywheel operated hand tools, each tool would suffer the disadvantages inherent in using battery power. The battery voltage varies as a function of the amount of charge remaining and the amount of electrical current being drawn. The rotary speed of the flywheel varies with the battery voltage, and thus the depth of drive of the fastener would unacceptably vary. The generally known controllers for corded flywheel operated hand tools are unable to accommodate these power variations.
Furthermore, even for a specific application, the desired depth of drive is affected by the type of work piece into which the fastener is driven and to user preferences. However, flywheel operated hand tools rely upon a given amount of kinetic energy imparted by the flywheel to achieve a desired depth of travel. Thus, when the work piece is more or less dense, the depth of the drive will vary. Moreover, the user may prefer in some instances to sink the fastener below the plane of the work piece or to leave the head of the fastener exposed for easy removal.
Other types of hand tools, such a pneumatic powered hand tools, generally rely on driving the fastener to a specific position in order to achieve a desired depth. For example, in U.S. Pat. Nos. 4,679,719, 5,732,870 and 5,918,788 a control module is described that advantageously determines the mode of operation for the trigger. In particular, a microprocessor provided additional capabilities by receiving two signal inputs initiated by the user and by selectively activating an electronic solenoid in response thereto. Although the increased functionality of the control module in such pneumatic tools has advantages, these control modules are not responsive to changes in operating conditions to vary the depth of drive.
Other tools employing a rotary member (e.g., drill) generally require the user to determine the proper speed of the tool. The user provides the closed loop control of the tool, monitoring the tool for binding and proper operation and depressing the trigger an appropriate amount. However, consistent operation of the tool is thus dependent upon the skill level and attentiveness of the user. Due to the speed in which a fastener must be driven into the workpiece, the user would only learn after the fact whether the rotary member (in this case a flywheel) was accelerated to an appropriate speed prior to firing.
Therefore, a significant need exists for a control module that drives medium and large fasteners into a work piece with a single driving action, yet has the increased portability of battery power. It would be further desired to have such a tool that consistently provides a depth of fastener regardless of the state of charge of the battery. It would be yet further desired to have a control module readily adapted to a family of hand tools.